Despite substantial interest in atypical nevi as melanoma risk factors and precursors, little is known about risk factors for these lesions, or their role in melanoma etiology. Previous case-control studies that have assessed atypical nevi as melanoma risk factors were small and/or clinic based. Similarly, only a few small, clinic-based studies have examined risk factors for atypical nevi. Our primary aims are to 1) conduct a large, population-based, case-control study of nonfamilial melanoma to evaluate atypical nevi, benign nevi, sun sensitivity, and solar exposure as risk factors, and 2) conduct a large, population-based evaluation of risk factors for atypical nevi. In separate analyses, we will explore risk factors associated with melanoma subgroups based on a) presence or absence of atypical nevi, and b) tumor histologic type. As a tertiary aim, we propose a validation substudy that will evaluate whether subjects can accurately self-diagnose atypical nevi. At least 535 cases of melanoma, ascertained through the NH State Cancer Registry, will be enrolled over a five year study period. We will enroll 800 population controls identified from drivers' license lists (age 65 or less), and medicare beneficiary lists (age greater than 65). Consenting subjects will complete a telephone interview, conduct skin self-examination, and participate in a dermatologist-conducted skin examination. Based on the dermatology examination, all subjects will be classified as "with" or "without" atypical nevi. Our statistical approach will include two primary case-control analyses to evaluate 1) risk factors for melanoma, and 2) risk factors for atypical nevi. In addition, we will conduct separate case-control comparisons to explore risk factors for specific melanoma subsets. Our approach will elucidate the etiology of melanoma, and identify risk factors for atypical nevi. Finally, we will evaluate subjects' ability to self-screen for atypical nevi by comparing the results of self-examination to the results of the dermatologist examination. The ability to self-diagnose atypical nevi has important implications for melanoma prevention.